Automotive vehicle air conditioning (A/C) systems require maintenance. Maintenance includes refrigerant recovery, evacuation, and recharging of the A/C system. Portable refrigerant recovery units are used in connection with this maintenance. The refrigerant recovery units connect to the A/C system of the automotive vehicle to recover refrigerant out of the system, separate out contaminants and oil, and recharge the system with additional refrigerant. As the automotive vehicle A/C systems decrease in size, it is increasingly important to recharge or refill the refrigerant systems with an accurate amount of refrigerant by weight.